My view on climate changehttps://ourchangingclimate.wordpress.com
Bart Verheggen's weblog on climate change issuesThu, 08 Feb 2018 21:11:13 +0000enhourly1http://wordpress.com/https://s2.wp.com/i/buttonw-com.pngMy view on climate changehttps://ourchangingclimate.wordpress.com
How blogs convey and distort scientific information about polar bears and Arctic sea icehttps://ourchangingclimate.wordpress.com/2017/12/22/how-blogs-convey-and-distort-scientific-information-about-polar-bears-and-arctic-sea-ice/
https://ourchangingclimate.wordpress.com/2017/12/22/how-blogs-convey-and-distort-scientific-information-about-polar-bears-and-arctic-sea-ice/#commentsFri, 22 Dec 2017 11:06:36 +0000http://ourchangingclimate.wordpress.com/?p=3170Our article on sea ice and polar bears proved to be a hot-button issue in the blogosphere. This was not entirely unexpected, of course. What is striking though, is that amidst all the criticism nobody has challenged our core finding: blogs on which man-made climate change and its impacts are downplayed are far removed from the scientific literature, at least regarding the topic of shrinking Arctic sea ice and the resulting future threat to polar bears.

Even more so, alternative figures that have been prepared by some critics basically underscore this same message (see examples below). That’s not so strange of course, since the signal is so clear: there is hardly any overlap between contrarian blogs and the scientific literature on this topic. Take a look at the pie-charts below for the three statements on sea ice and those on polar bears, for the two different groups of blogs (termed denier and science-based blogs, respectively), and the peer-reviewed scientific articles that investigate both polar bears and Arctic sea ice. This is basically an extension of figure 1 in the paper, in which only the two blog categories were shown. Most scientific articles as well as science-based blogs assess Arctic sea ice extent to be shrinking and polar bears to be threatened as a result, and most denier blogs take a contrary view on both sea ice and polar bears. They are poles apart.

You may argue that it was overkill to use an elaborate statistical analysis such as PCA on this dataset. It was used mainly to visualize our results in one figure. All the criticism on the PCA and the details of how data were analyzed misses the forest for the trees: there is a clear distinction between blogs, where the group that accepts AGW appears to base their claims on peer-reviewed science, and the group that doesn’t accept AGW does not. The latter group appear to base their claims to a large extent on blogs written by one particular biologist, Susan Crockford, whose views run counter to the relevant ecological literature.

Our paper is first and foremost a characterization of the blogosphere, and how it compares to the scientific literature. We restricted our literature search to scientific articles that investigate both polar bears and sea ice, and that shed light on polar bear ecology and how it may or may not depend on the presence of sea ice. An article such as “Evolutionary roots of iodine and thyroid hormones in cell signaling” does not fit that bill, to name just one example of Crockford’s scientific articles that has been pointed out as evidence of her having published on polar bear ecology. She has not.

Even though it is not the main scope of our paper, we described the scientific context of polar bear ecology and explained how and why polar bears depend on their sea ice habitat (summarized in my previous blog post). As such, we argued that the scientific understanding of arctic sea ice decline and polar bear ecology is more credible than the viewpoints put forward on contrarian blogs. However, providing new ecological evidence was not the point of this paper. The point was to investigate how our current ecological understanding is conveyed and distorted in the blogosphere.

If some people think that our conclusion is wildly wrong, then they could at least show some evidence to prove their point, right? They probably realize that our conclusion is robust, so instead they try to nitpick on details and make it appear as if that undermines our conclusion. It does not.

Appendix: A collection of PCA graphs depicting our results, all basically underscoring the main conclusion that one group of blogs correctly conveys our current scientific understanding, while another group of blogs distort this understanding and promotes a very different viewpoint regarding sea ice and polar bears.

From top to bottom the following PCA figures are shown:

As published in the Bioscience paper, in which missing values are replaced by zero after scaling the data

As mentioned in the supplemental information with our paper, jittering was applied to our PCA figure to gently offset data with the exact same entries from each other for graphical purposes. Tol uses an alternative method to provide information on sample size for specific data entries, namely via the size of the symbol used in the figure. Whatever your preference, the conclusion drawn from these figures is the same: there is a clear gap between the consensus in the scientific literature and science-based blogs on the one hand, and contrarian blogs on the other hand. We thank Roman Mureika and Richard Tol for underscoring the validity of our conclusion.

]]>https://ourchangingclimate.wordpress.com/2017/12/22/how-blogs-convey-and-distort-scientific-information-about-polar-bears-and-arctic-sea-ice/feed/618BartThere once was a polar bear – science vs the blogospherehttps://ourchangingclimate.wordpress.com/2017/11/29/there-once-was-a-polar-bear-science-vs-the-blogosphere/
https://ourchangingclimate.wordpress.com/2017/11/29/there-once-was-a-polar-bear-science-vs-the-blogosphere/#commentsWed, 29 Nov 2017 17:07:20 +0000http://ourchangingclimate.wordpress.com/?p=3145Blogs on which man-made climate change and its impacts are downplayed are far removed from the scientific literature. That is the conclusion of a new article in Bioscience in which a variety of blogs was compared with the scientific literature regarding the shrinking Arctic sea ice and the impact on polar bears.

Jeff Harvey, a Canadian ecologist working at the Netherlands Institute for Ecology (NIOO-KNAW) and the Free University of Amsterdam (VU), set out to investigate how the information on blogs relates to the scientific literature. The focus was on conclusions about Arctic sea ice and polar bears. The results have been published in the article “Internet Blogs, Polar Bears, and Climate-Change Denial by Proxy” in the journal Bioscience. Disclaimer: I’m a co-author of said article.

So what did we find? There is a clear separation amongst blogs, where approximately half of the 90 blogs investigated agree with the majority of the scientific literature, whereas other blogs took a position that is diametrically opposed to the scientific conclusions. Most of the blogs in the latter group based their opinions on one and the same source: Susan Crockford.

90 blogs and 92 scientific articles were classified according to six statements about Arctic sea ice and polar bears and the citation of Crockford. The figure shows the results of a principal component analysis (PCA) of the results. PCA is a technique to show the maximum amount of variation in a dataset with a minimum of newly defined parameters, the so-called principal components. The score on PC1 shows a separation between on the one hand the position that Arctic sea ice extent is shrinking and that this poses a threat to polar bears (most scientific articles and science-based blogs) and on the other side the position that Arctic sea ice is not shrinking or that it’s due to natural variability and that polar bears are not threatened (pseudo-skeptical blogs).

Arctic Sea ice

Arctic sea ice has shrunk dramatically in the past few decades, both in surface area and in thickness. This trend is expected to continue with ongoing global warming as a result of greenhouse gas emissions. Of course the decrease in sea ice doesn’t happen monotonically, but rather with ups and downs as a result of natural variability. When it happens to fit their perspective, such short term fluctuations are framed as a ‘recovery’ on certain blogs, or the decrease in Arctic sea ice is downplayed in other ways.

Polar bears

Polar bears depend on sea ice for catching their main prey, seals. So their habitat literally melts away as temperatures rise. Over time, polar bears have become iconic symbols of the negative effects of global warming. The population has been relatively stable so far, but you can’t just extrapolate that to the future. Biological impacts are often non-linear, and their dependence on sea ice means that in the future polar bears will likely face difficulties from continuing warming trend. Indeed, they have been classified as ‘vulnerable’ by the International Union for the Conservation of Nature (IUCN) and as ‘threatened’ under the US Endangered Species Act.

“No climate report is complete without an obligatory photo of a polar bear balancing on a piece of ice”, John Oliver said in the famous 97% episode of “Last Week Tonight”.

But what about the previous interglacial?

The polar bear species has survived the previous interglacial ~125,000 years ago. Some deduce from that that the polar bear will be fine. However, if CO2 emissions aren’t drastically reduced temperatures will get a lot warmer over the coming centuries and even millennia than during the previous interglacial. Moreover, during the previous interglacial summers were probably not completely ice-free, as is expected to happen later this century as a consequence of continuing warming (which of course depends on how global emissions evolve). The current warming trend is many times faster than back then, making potential adaptation to new conditions more difficult. Besides shrinking sea ice there are currently also other factors that negatively affect polar bears, such as human settlements, industrial activities, hunting, bio-accumulation of toxins, and smaller seal populations.

Blogs

A future with ‘business as usual’ emissions doesn’t look bright for the polar bear. Blogs appear to fall into two camps in how they write about this topic. On pseudo-skeptical blogs scientific uncertainty is twisted into ignorance, or the current situation is extrapolated into the future without taking into account the available knowledge of polar bear ecology. They usually don’t base themselves on the scientific literature, but rather on the statements of one person. These rather unfounded opinions are consequently recycled via the blogosphere, which in this respect acts as an echo-chamber. Susan Crockford writes a lot about polar bears, but does so mostly on her own website and for anti-mitigation thinktanks such as the Heartland Institute and the Global Warming Policy Foundation (GWPF); not in the scientific literature.

The gap between scientific conclusions and pseudo-skeptical blogs will not be a great surprise to those who closely follow both the scientific and the public debate about climate change. After all, this tendency is more generally visible than only on the topic of Arctic sea ice and polar bears. This is however the first time that this has been demonstrated on the basis of a systematic comparison between the scientific literature and blogs. To close the consensus gap the authors call on their fellow scientists to actively participate in the public debate.

The Supplementary Information that was part of the paper submission is still not available on the OUP website despite our repeated request to do so asap. In the meantime you may download the SI here. The data (scores per blog and per scientific article) are available via Dryad.

There has been quite some media attention for this study. Below an incomplete listing (for Dutch pieces see the abovementioned link to my Dutch sister-blog).

The documentary “The uncertainty has settled” from Dutch filmmaker Marijn Poels follows him on his journey in rural Austria and Germany to witness how energy policies impact traditional agriculture. That is the stepping stone to also look into different ideas about how and why the climate is changing. Unfortunately Poels has no clue how to distinguish fact from fiction, and by his own admission he has no interest in making that distinction. As a result the documentary offers a mix of basic scientific insights, plain falsehoods, and misleading statements regarding climate science. As an unwitting viewer you are left utterly confused –cued by Poels’ facial expression at those times- how to reconcile these seemingly opposing viewpoints. Creating confusion was apparently his objective (as he acknowledges on his website), but it makes for a surreal experience if you know you’re being fooled. I think spreading falsehoods is doing a disservice to the public, as I’ve said to Marijn Poels during a radio-debate (in Dutch).

Let’s look more closely at some of the things being said about climate change in the documentary.

Marijn Poels meets another Dutchman in rural Germany, who laments how climate policies have led to the disappearance of local nature. He says it’s insane to think that a CO2 concentration as low as 0.035% (currently 0.04%) could have any impact on climate. That’s clearly fallacious reasoning (argument from incredulity): there are plenty of examples of compounds that have serious impacts at the same or lower concentrations (e.g. a CO detector will sound the alarm at such a concentration and you had better leave the premises). Without any CO2 in the air the globe would quickly become a frozen ball of ice, since the main air constituents (nitrogen 78%, oxygen 21%, argon 1%) don’t impede the infrared heat loss to space.

Later in the documentary he meets with climate scientist Hans von Storch, astrophysicist Piers Corbyn and physicist Freeman Dyson. Those in the loop will immediately recognize that this is not at all a fair representation of the scientific debate, but rather provides a very skewed vision thereof by emphasizing outlier views that are demonstrably false.

Hans von Storch accurately describes our current knowledge about climate change: We know that the earth has warmed and we can’t explain this warming without considering the human-induced increase in greenhouse gases in the atmosphere. He also distinguishes how scientific knowledge may be very uncertain in specific details, while the core tenets are robustly known: “The fact that CO2 has a significant influence on climate is indisputable.”

It’s astonishing how many falsehoods and conspiracy theories Piers Corbyn mentions over the course of few minutes. Some of the things he said:

FALSE: The increasing CO2 concentration in the atmosphere is coming from the oceans

If Corbyn were right, the concentration in the ocean should have decreased in order to explain the increased atmospheric concentration (a simple consequence of conservation of mass). However, CO2 concentrations have been observed to increase both in the atmosphere and in the ocean. In reality, the excess CO2 in both atmosphere and ocean originates from fossil fuel burning, as is evident from the isotopic signature and the concomitant decrease in atmospheric O2 concentration.

FALSE: CO2 only follows temperature

During the ice age cycles CO2 acted as an amplifying feedback on the warming which was initiated by changes to the earth’s orbit. During those times of relatively slow warming the temperature indeed started to increase before the CO2 concentrations did, after which the CO2 caused even more warming. Hence it’s a bit of a chicken-egg issue with CO2 and temperature, but Corbyn’s statement is misleading. The current CO2 increase is unequivocally anthropogenic and ~100 times faster than it was in glacial to interglacial transitions. Moreover, we have known since the mid-nineteenth century that CO2 absorbs infrared radiation and thus acts as a greenhouse gas which impedes planetary heat loss and thus warms up the surface.

CONSPIRACY THEORY: The increased temperatures are a result of fraud with the observations

Globally averaged temperatures are computed independently by a number of different research group and they all agree within a close margin of each other. The raw data are available, so everyone who’s interested and who has the requisite skill can try to reproduce (or falsify) these calculations. A number of ‘skeptical’ people have indeed done so, and lo and behold, they found the same result: the globe really is warming.

Corbyn continues with his conspiracy theories and doesn’t even seem bothered that they’re mutually inconsistent with each other: on the one hand he claims that the ‘climate ideology’ has been made up by international big business interests, on the other hand he also claims that the ‘myth of climate change’ is a scheme to de-industrialize the West. How can you possibly take someone like this seriously?

Next up is renowned physicist Freeman Dyson, who is very skeptical of the ability of climate models to make accurate projections of future warming. In the documentary he paints a false dichotomy between observations on the one hand and models on the other hand, whereas in modern science they really go hand in hand and models form an integral part of science. Model simulations agree very well with observations, despite Dyson’s claims to the contrary. For good measure he also throws in a conspiracy theory by claiming that climate modelers only want to scare people, because they wouldn’t get money for their research otherwise. This goes to show that otherwise brilliant people can still make silly claims about a field of science that they don’t know much about.

So why did Marijn Poels chose to interview people who are demonstratively wrong (and who are not actually climate scientists)? His whole idea with the documentary was as a personal quest in which he listened to various viewpoints without judgment or evaluation. In a radio-debate I did with him on Dutch Radio NPO1 he proclaimed that he doesn’t feel any responsibility to figure out who’s talking sense and who’s talking nonsense. On twitter he has since confirmed that he doesn’t care what true and what’s not. I find that a very strange attitude for a documentary-maker, as I tried saying at the end of the radio-debate:

Scientists are seeking a better understanding of the world around us. What I hear Marijn Poels say is that it doesn’t matter to him what’s true and what’s not. That goes against everything I value as a scientist.

He also tweeted that “if there are multiple scientific perspectives, then it’s worthy of debate”. So the problem is not only that he doesn’t care about whether something is true or not; he doesn’t see that some of what he calls “scientific perspectives” are plain untruths. Claiming that the CO2 might just have come out of the ocean is no more a ‘scientific perspective’ than claiming that vaccines cause autism or that smoking is not linked to cancer. Science has conclusively shown these statements to be false.

In a public debate about smoking regulation there’s no point in discussing whether smoking is really bad for you: we know that by now, based on scientific evidence.

Likewise, in a public debate about climate policies there’s no point in discussing whether CO2 really contributes substantially to climate change: we know that by now, based on scientific evidence.

]]>https://ourchangingclimate.wordpress.com/2017/07/17/a-critical-look-at-the-uncertainty-has-settled-documentary-by-marijn-poels/feed/14BartI’ll march for science, because the truth and the pursuit of truth matters. A lot.https://ourchangingclimate.wordpress.com/2017/04/20/march-for-science-pursuit-of-truth-not-just-another-opinion/
https://ourchangingclimate.wordpress.com/2017/04/20/march-for-science-pursuit-of-truth-not-just-another-opinion/#commentsThu, 20 Apr 2017 20:18:54 +0000http://ourchangingclimate.wordpress.com/?p=3116This saturday 22 April a global March for Science will take place in around 500 hundred cities worldwide. I’ll take part in the Amsterdam March for Science, taking place between 12:00 and 16:00 on Museumplein. You can find me in the “discovery” tent with some posters about climate change and sustainable energy.

Science and rational thinking has brought a lot of good to the world. Facts and a good understanding of the situation are important input for making wise decisions. Scientists should be able to do their work in freedom, not being hindered or silenced by political pressure. Science is not just another opinion. I value the truth and the pursuit of truth. That’s why I will join the march for science.

Great 4 minute video by Neil deGrasse Tyson about the value of science:

“You are only entitled to what you can argue for. (…) false equivalence between experts and non-experts is an increasingly pernicious feature of our public discourse. (…) If ‘Everyone’s entitled to their opinion’ just means no-one has the right to stop people thinking and saying whatever they want, then the statement is true, but fairly trivial. No one can stop you saying that vaccines cause autism, no matter how many times that claim has been disproven. But if ‘entitled to an opinion’ means ‘entitled to have your views treated as serious candidates for the truth’ then it’s pretty clearly false. And this too is a distinction that tends to get blurred.”

]]>https://ourchangingclimate.wordpress.com/2017/04/20/march-for-science-pursuit-of-truth-not-just-another-opinion/feed/9BartEarth’s temperature over the past two million yearshttps://ourchangingclimate.wordpress.com/2016/10/06/earths-temperature-over-the-past-two-million-years-snyder-earth-system-sensitivity/
https://ourchangingclimate.wordpress.com/2016/10/06/earths-temperature-over-the-past-two-million-years-snyder-earth-system-sensitivity/#commentsThu, 06 Oct 2016 20:38:46 +0000http://ourchangingclimate.wordpress.com/?p=3079A new reconstruction of global average temperature over the past two million years has recently appeared in Nature (Snyder, 2016). That is quite a feat and a first for this duration. The figure below, made by Jos Hagelaars, shows Snyder’s temperature reconstruction, combined with the observed warming since 1880 and projected warming until the year 3000 for two IPCC scenarios, RCP6.0 and RCP8.5.

The RCP8.5 can be viewed as a “no mitigation” scenario, whereas RCP6.0 would be a “limited mitigation” scenario. It is clear that in both scenarios global warming over the next centuries will take us out of the temperature realm of the past two million years. A similar figure (which I tweeted yesterday) but then with temperature projections stopping in the year 2100 can be found here.

Even though lauded as a very valuable and novel contribution to the field, Snyder’s reconstruction has also been criticized because the temperature amplitude between glacial and interglacial states appears relatively large (~6 degrees) compared to other recent reconstructions, e.g. by Shakun et al (2012) (~4 degrees). Somewhat related, Snyder estimates the global average temperature during the previous interglacial (Eemian) to be warmer than now, whereas e.g. Hansen et al (2016, under review) argue that they are similarly warm. By the way, sea levels were 6 to 9 metres higher in the Eemian than now. Sea level responds very slowly to a change in temperature, yet another sign of the vast inertia in the climate system.

Somewhat overshadowing the actual temperature reconstruction that Snyder presented was her calculation of an earth system sensitivity (ESS) based on a correlation between temperature and CO2 over the past few glacial cycles. The earth system sensitivity denotes the long-term temperature response to a doubling in CO2 concentrations, including e.g. the response of ice sheets (which is typically excluded from the more often used equilibrium climate sensitivity, ECS). She then applied the ESS value of a whopping 9 degrees, obtained from this simple correlation, to the current warming, stating in the abstract:

This result suggests that stabilization at today’s greenhouse gas levels may already commit Earth to an eventual total warming of 5 degrees Celsius (range 3 to 7 degrees Celsius, 95 per cent credible interval) over the next few millennia as ice sheets, vegetation and atmospheric dust continue to respond to global warming.

Where “commit” means that this level of warming would be eventually expected based on current CO2 concentrations.

The reason why I think it’s wrong is that in her calculation of ESS she takes the radiative forcing caused by albedo changes (resulting from the massive change in ice coverage between a glacial and interglacial state) and assumes it to be a feedback on the CO2 induced temperature-change.

There are two issues with this:

1) In reality both the changes in albedo (reflectivity) and CO2 concentration are feedbacks on the orbital forcing, and the relation in the one direction (a change in earth’s orbit causing a temperature change which in turn causes albedo and CO2 levels to change) is not necessarily the same as the relation in the reverse direction, as is currently happening with human-induced increases in CO2. Gavin Schmidt makes this point in two consecutive posts at RealClimate (here and here), though you might also want to read Hansen’s take, who has used a similar approach as Snyder did).

2) The ESS value obtained would (ignoring the more complex first point) perhaps be applicable to a glacial-interglacial transition, but decidedly not to an interglacial-‘hyperinterglacial’ transition, where the ice-albedo feedback would of course be much smaller because of the much smaller ice-covered surface area.

This second point was also made by James Annan in response to Hansen’s 2008 Target CO2 paper, where he essentially used the same method as Snyder is using (but came to a smaller ESS value of 6 degrees, because Snyder uses a greater temperature-amplitude between glacial-interglacial). Hansen noted in his paper though that “The 6°C sensitivity reduces to 3°C when the planet has become warm enough to lose its ice sheets.”

In other words, using Snyder’s very (and probably too) high ESS value to project future warming is unwarranted and wrong.

]]>https://ourchangingclimate.wordpress.com/2016/10/06/earths-temperature-over-the-past-two-million-years-snyder-earth-system-sensitivity/feed/4Bartsnyder-et-al-2016-rcp8-5-rcp6-0-nr3Shakun_Marcott_HadCRUT4_A1B_EngClimate inertiahttps://ourchangingclimate.wordpress.com/2016/08/09/climate-inertia/
https://ourchangingclimate.wordpress.com/2016/08/09/climate-inertia/#commentsTue, 09 Aug 2016 14:05:49 +0000http://ourchangingclimate.wordpress.com/?p=3046Imagine you’re on a supertanker that needs to change its direction in order to avoid a collision. What would you do? Would you continue going full steam ahead until you can see the collision object right in front of you? Or would you try to change course early, knowing that changing a supertanker’s course takes a considerable amount of time?

The supertanker’s inertia means that you have to act in time if you wish to avoid a collision.

The climate system also has a tremendous amount of inertia built in. And like with the supertanker, this means that early action is required if we want to change the climate’s course. This inertia is a crucial aspect of the climate system, both scientifically but also societally – but in the latter realm it’s a very underappreciated aspect. Just do a mental check: when did you last hear or read about the climate’s inertia in mainstream media or from politicians?

The inertia of the climate system could be compared to that of a supertanker: if we want to change its course, it’s important to start steering the wheel in the desired direction in time.

Why is it so important? Because intuitively many people might think that as soon as we have substantially decreased our CO2 emissions (which we haven’t), the problem will be solved. It won’t, not by a very long shot. Even if we reduce CO2 emissions to zero over a realistic timeframe, the CO2 concentration in the atmosphere – and thus also the global average temperature- will remain elevated for millennia, as can be seen in the figure below. The total amount of carbon we put in the atmosphere over the course of a few hundred years will affect life on this planet for hundreds of thousands of years. And if we want to reduce the amount of warming that we commit the future to, we need to reduce our carbon emissions sooner rather than later. The longer we postpone emission reductions, the stronger those emissions reductions would need to be in order to have the same mitigating effect on long-term warming.

That’s why climate inertia is so important.

Modeled response of the atmospheric CO2 concentration (panel b) and surface air temperature compared to the year 2000 (panel c) to prescribed CO2 emissions (panel a). The CO2 concentration remains elevated long after CO2 emissions have been reduced, because the long-term sinks for CO2 operate very slowly (see e.g. IPCC FAQ 6.2 for an explanation of these carbon sinks). Since CO2 impedes infrared heat loss, for millennia the globe will remain warmer than it was before CO2 concentrations rose. The temperature lags behind the CO2 concentration because of the time it takes for the oceans to warm up. Figure from Zickfeld et al (2013).

As I wrote before: Postponing meaningful mitigation action until the shit hits the fan comes with considerable risk, because many changes in climate are not reversible on human timescales. Once you notice the trouble, it’s only the beginning, because of the inertia in the various systems (energy system, carbon cycle and climate system). The conundrum is thus that those who caused the problem are in the best position to solve it, but since the full consequences will not materialize until much later, they have the least incentive to do so.

Over at Bits of Science two Dutch science journalists, Rolf Schuttenhelm and Stephan Okhuijsen, published an interesting piece that focuses on the same issue: we only see a portion of the warming that we have committed ourselves to, due to the thermal inertia provided by the oceans. Just as a pot of water doesn’t immediately boil when we turn on the stove, the oceans take time to warm up as well. And since there’s a lot of water in the oceans, it takes a lot of time.

They included the following nifty graph, with the observed surface temperature but also the eventually expected temperature at the corresponding CO2 concentration (which they dub the ’real global temperature’), based on different approaches to account for warming in the pipeline:

This is a nice way to visualize the warming that’s still in the pipeline due to ocean thermal inertia. From a scientific point of view the exact execution and framing could be criticized on certain aspects (e.g. ECS is linearly extrapolated instead of logarithmically; the interpretation that recent record warmth are not peaks but rather a ‘correction to the trend line’ depends strongly on the exact way the endpoints of the observed temperature are smoothed; the effect of non-CO2 greenhouse gases is excluded from the analysis and discussion), but the underlying point, that more warming is in store than we’re currently seeing, is both valid and very important.

Update: ClimateInteractive has a good simulation of how this inertia works out in practice. By moving the slider at the bottom the figure you can choose between different emission scenarios. In the graphs above you then see the effect this has on the CO2 concentration, the global average temperature, and the sea level, and how this response is damped. The further down the cause-effect chain, the more damped – or better: the more slowed down- the response is. The sea level will continue to rise the longest (even long after the temperature has stabilized or even starts decreasing), but will take a while to get going. This simulation only runs to the year 2100 though.

]]>https://ourchangingclimate.wordpress.com/2016/08/09/climate-inertia/feed/19BartInertiaZickfeld 2013real-global-temperature-graph - Bits of ScienceNew survey of climate scientists by Bray and von Storch confirms broad consensus on human causationhttps://ourchangingclimate.wordpress.com/2016/06/22/new-survey-of-climate-scientists-by-bray-and-von-storch-confirms-broad-consensus-on-human-causation/
https://ourchangingclimate.wordpress.com/2016/06/22/new-survey-of-climate-scientists-by-bray-and-von-storch-confirms-broad-consensus-on-human-causation/#commentsWed, 22 Jun 2016 15:57:30 +0000http://ourchangingclimate.wordpress.com/?p=2941Bray and von Storch just published the results of their latest survey of climate scientists. It contains lots of interesting and very detailed information, though some questions are a little biased in my opinion. Still, they find a strong consensus on human causation of climate change: 87.4% of respondents are to some extent convinced that most of recent or near future climate change is, or will be, the result of anthropogenic causes (question v007). Responses were given on a scale from 1 (not at all) to 7 (very much). In line with Bray (2010) a response between 5 and 7 is considered agreement with anthropogenic causation. In their 2008 survey the level of agreement based on the same question was 83.5% and in 2013 it was 80.9%.
How convinced are you that most of recent or near future climate change is, or will be, the result of anthropogenic causes? (v007) not at all 1 2 3 4 5 6 7 very much

Question v013 asked a somewhat similar question as we did in our 2012 climate survey, namely the percentage of global warming that is attributable to human activities:

Since 1850, it is estimated that the world has warmed by 0.5 – 0.7 degrees C. Approximately what percent would you attribute to human causes? (v013)1=0% 2=1-25% 3=25-50% 4=51-75% 5=76-100%

84.2% of respondents picked one of the two answer options that correspond to the canonical “more than half” or “most” of global warming that according to the IPCC is human caused. However, the corresponding IPCC statement is with regards to warming since the 1950’s, about which there is a lot more confidence, whereas this question specifies the warming since 1850.

But wait a moment, hasn’t the earth warmed a lot more than 0.5-0.7 degrees C since 1850? Yes, it definitely has; we’ve recently breached the 1 degree mark relative to the 1850-1880 average, so the range given in their question is quite outdated. A defensible choice at the time of drafting the survey would have been to quote the latest IPCC number of 0.85 (0.65 to 1.06) degrees warming over the time period 1880-2012, even if current temperatures have gone up sharply since then.

Global average surface temperature relative to the 1850-1880 mean. Last annual average shown is 2015; if the first few months of 2016 are a guide, the vertical scale might have to be adapted for 2016. Figure by Jos Hagelaars.

Moreover, the answer options for v013 do not cover the full range of possibilities. Natural factors could have caused warming or cooling. Imagine that natural factors would have caused a cooling of 0.1 degrees C since pre-industrial times (which is not at all implausible), then to achieve closure with the observed warming of 1.0 degrees, anthropogenic factors should have contributed 1.1 degrees, or 110% of the observed warming. We discussed this argument in detail in our ES&T paper emanating from the climate science survey we conducted in 2012.

I emailed Dennis Bray about these and other issues after having responded to their survey back in 2015. He defended their choice of lowballing the observed warming as being consistent with their previous surveys and not being much different from more recent, and also likely contested, estimates. Strangely, he disagreed with the possibility of a factor being responsible for more than 100% of the observed warming, even in the hypothetical example above.

Cook et al (myself included) recently wrote an article in which we reviewed the existing ‘consensus’ estimates. This latest Bray and von Storch survey finds a level consensus on attribution that is consistent with other studies, though towards the lower end of the range. From their description I don’t think there is a bias in their sample of scientists, though there is always the possibility of self-selection, where people might be more likely to respond to a survey if it originates from a source who they perceive to be credible. Repeatedly, surveys have found that the level of consensus goes up as you zoom in to a sample of scientists with more relevant expertise. The Bray and von Storch results, as are ours, are mostly representative of a broad group of climate related scientists.

A detail of particular interest to me is that the survey questions included the response option “no answer”. That explains the different sample size for different questions (“Number of obs”). It’s probably no coincidence that question v013 (asking for a specific range of percent contribution) has a smaller sample size (n=587), and by inference more “no answer” responses, than the other, but simpler, attribution question v007 (n=640). This is consistent with what we found in our 2012 climate science survey: fewer respondents picked a specific percentage range of attribution compared to providing a qualitative judgment thereof. Though admittedly “no answer” (in the Bray and von Storch survey) is less ambiguous in this context than “I don’t know”, “unknown” or “other” (in our survey).

Amidst the questions on science and society I perceived some questions to have an “anti-consensus” (v069) or “anti-alarmist” (v067) tone to it, but there were no questions asking for mirror image perceptions. Doomsday stories need to be investigated before they get out of hand (v067): of course. But no question was asked whether stories downplaying a scientifically established risk should be investigated. I would have likewise responded: of course. To his credit, Dennis Bray acknowledged in his email that this was an oversight on their part.

]]>https://ourchangingclimate.wordpress.com/2016/06/22/new-survey-of-climate-scientists-by-bray-and-von-storch-confirms-broad-consensus-on-human-causation/feed/24BartBray and von Storch 2015 - v007 how convinced are you that most of recent and future GW is or will be the result of anthropogenic activityBray and von Storch 2015 - v013 What percentage of global warming since 1850 do you attribute to human causesHadCRUT4_Ref_1850_tm_1880Consensus on consensus: a synthesis of consensus estimates on human-caused global warminghttps://ourchangingclimate.wordpress.com/2016/04/13/consensus-on-consensus-a-synthesis-of-consensus-estimates-on-human-caused-global-warming/
https://ourchangingclimate.wordpress.com/2016/04/13/consensus-on-consensus-a-synthesis-of-consensus-estimates-on-human-caused-global-warming/#commentsWed, 13 Apr 2016 00:02:00 +0000http://ourchangingclimate.wordpress.com/?p=2901Most scientists agree that current climate change is mainly caused by human activity. That has been repeatedly demonstrated on the basis of surveys of the scientific opinion as well as surveys of the scientific literature. In an article published today in the journal Environmental Research Letters (ERL) we provide a review of these different studies, which all arrive at a very similar conclusion using different methods. This shows the robustness of the scientific consensus on climate change.

This meta-study also shows that the level of agreement that the current warming is caused by human activity is greatest among researchers with the most expertise and/or the most publications in climate science. That explains why literature surveys generally find higher levels of consensus than opinion surveys. After all, experienced scientists who have published a lot about climate change have, generally speaking, a good understanding of the anthropogenic causes of global warming, and they often have more peer-reviewed publications than their contrarian colleagues.

Figure: Level of consensus on human-induced climate change versus expertise in climate science. Black circles are data based on studies of the past 10 years. Green line is a fit through the data.

The video below provides a great overview of the context and conclusions of this study:

Surveys show that among the broad group of scientists who work on the topic of climate change the level of consensus is roughly between 83 and 97% (e.g. Doran, Anderegg, Verheggen, Rosenberg, Carlton, Bray, Stenhouse, Pew, Lichter, Vision Prize). If you zoom in on the subset of most actively publishing climate scientists you find a consensus of 97% (Doran, Anderegg). Analyses of the literature also indicate a level of consensus of 97% (Cook) or even 100% (Oreskes). The strength of literature surveys lies in the fact that they sample the prime locus of scientific evidence and thus they provide the most direct measure of the consilience of evidence. On the other hand, opinion surveys can achieve much more specificity about what exactly is agreed upon. The latter aspect – what exactly is agreed upon and how does that compare to the IPCC report- is something we investigated in detail in our ES&T article based on the PBL survey.

As evidenced by the many –unfounded- criticisms on consensus studies, this is still a hot topic in the public debate, despite the fact that study after study has confirmed that there is broad agreement among scientists about the big picture: our planet is getting warmer and that is (largely) due to human activity, primarily the burning of fossil fuels. A substantial fraction of the general public however is still confused even about the big picture. In politics, schools and media climate change is often not communicated in accordance with the current scientific understanding, even though the situation here in the Netherlands is not as extreme as e.g. in the US.

Although science can never provide absolute certainty, it is the best method we have to understand complex systems and risks, such as climate change. If you value science it is wise not to brush aside broadly accepted scientific insights too easily, lest you have very good arguments for doing so (“extraordinary claims require extraordinary evidence”). I think it is important for proper democratic decision making that the public is well informed about what is scientifically known about important issues such as climate change.

A new study released by NASA scientist Jay Zwally and colleagues in the Journal of Glaciology, receiving wide coverage in the media last month, reports an 82 Gigatons per year increase of land ice in Antarctica during the period 2003-2008. The study received much skepticism from other leading scientists in the field, as there are many indications that point at the contrary: ice loss, possibly irreversible. How does this new study fit in that picture, what are the consequences for expected sea level rise and are these numbers correct? Glaciologist and polar scientist Jan Wuite, working at Enveo in Innsbruck and involved in various international studies related to Antarctica explains.

One of the adverse consequences of climate change is global sea level rise. At more than 3 mm per year, the current sea level rises twice as fast as during the 20th century. The expectations are a rise of at least 70 cm by the turn of this century. The principal causes are clear: global decline of land ice (mountain glaciers & ice sheets) and thermal expansion of ocean water (water expands as it becomes warmer). To clarify, land ice is resting on land and can reach a thicknesses of up to several kilometers, in contrast to seasonally restricted sea ice (mainly just frozen ocean water), that is typically only a few meters thick and has no direct influence on sea level. Studies have indicated an increasing contribution of the two largest ice sheets, the Greenland and Antarctic ice sheets, to sea level rise.

The largest unknown for future sea level rise is caused by uncertainty in the predicted response of the Antarctic ice sheet to global warming. As warmer air can hold more moisture, it is possible that increasing snow accumulation compensates part of the sea level rise. On the other hand it is also possible that ice drains faster to the oceans accelerating it.

There is a lot of ice in Antarctica; in some places the ice thickness reaches well over 4 km. There is enough ice to, when melted completely, raise global sea levels with roughly 58 m. But even if only a small part of that melts it could have a significant impact on coastal communities, or ocean circulation. For this reason scientists are very interested in mass changes of the ice sheets: the mass balance.

First of all, how do scientists actually measure these changes? Because of the remoteness and vastness of Antarctica, satellite observation is the only feasible way to study the ice sheet. On a smaller scale these measurements are supported by airborne and field data. Three principal methods are used: satellite altimetry, satellite gravimetry and the so-called input-output method (IOM).

In the IOM approach, as the name implies, estimates of the total ice input – the net snow accumulation or surface mass balance – are compared with estimates of the discharge of ice to the ocean (output). The discharge is calculated combining surface velocity measurements with ice thickness estimates. The independent and relative new gravimetry method determines changes in the ice mass directly by measuring tiny fluctuations in the earth’s gravity field. Satellite altimetry uses very precise repeat elevation measurements of the ice surface to determine volume changes. These volume changes can then be converted to ice mass using estimates of the density. Each of the methods has its strengths and weaknesses. In the study from Zwally and colleagues only the last so-called volumetric method is used.

Ice gain

In his study Zwally uses data from different satellites for two periods: the ESA radar satellites ERS-1 and ERS-2 during the period 1992-2001 and the NASA laser satellite ICESat during 2003-2008. The surface elevation measurements are used to create maps of annual elevation change. These maps must be corrected for processes that do not influence the total ice mass, such as for instance firn densification (compacting of the upper layers of the ice sheet as the air is squeezed out) and to a lesser degree vertical movement of the bedrock underneath the ice sheet in response to changing ice masses. After the correction the remainder elevation change is caused by either short-term variations in snowfall on the one hand or dynamic changes of the ice sheet on the other hand. The latter are related to ice flow velocity and reflect the ice sheets slow response to changing boundary conditions such as climatic changes. A crucial step is to convert the volumetric changes to ice mass using density estimates. In this study meteorological models are used to separate the part caused by accumulation changes (with the lower density of snow), leaving in theory the part caused by dynamic changes (with the density of pure ice). Using this approach the scientists come to the surprising finding that during the study period (1992-2008) increasing ice losses in the coastal areas of West Antarctica and the Antarctic Peninsula are entirely compensated for by ice growth in interior West Antarctica and the much larger East Antarctic Ice Sheet. In other words, according to Zwally and colleagues the total (land) ice mass of Antarctica is increasing, buffering part of the – independently determined – global sea level rise. The authors caution that under current conditions this could change within the coming decades.

Criticism

The study from Zwally and colleagues drew a lot of criticism, as the claims contradict a decade of studies and measurements. One of the main arguments is that the used data and method is not accurate enough to support such firm conclusions. The signal scientists are trying to measure is only in the order of a few centimeters. Because of the vastness of the ice sheet, tiny errors or wrong assumptions could translate into huge quantities giving entirely different results. For this reason multi-disciplinary studies that try to reconcile mass balance estimates using different independent methods are deemed more reliable. Just a few years ago such a study reconciling ice sheet mass balance estimates was published in the prestigious scientific journal Science. The study, a collaboration of many research groups (including the group of Zwally) compared estimates of ice sheet mass balance derived from the three independent methods as described above. The outcome was an unambiguous ice loss in Antarctica. The slight gain in East Antarctica, in particular Dronning Maud Land since 2009, did not outweigh the tremendous loss in other parts of Antarctica. The consensus was a net ice loss of 71 Gigatons per year for Antarctica as a whole. Moreover the period of observations was longer running from 1992 to 2011.

Nevertheless, even at that time there was an unsatisfactory spread in mass balance estimates, in particular for East Antarctica. The authors recommended acquisition of additional measurements with denser spatial and temporal sampling. The CryoSat-2 satellite, launched in 2010, adhered to this recommendation and subsequential mass balance estimates, that used this new altimetric satellite but also gravimetric satellites, confirmed earlier findings of overall ice loss in Antarctica. Moreover, the ice loss even appeared to accelerate. For example a study published last year by McMillan and collegues, that used CryoSat-2 data, reported a total ice loss of 159 Gigatons per year between 2010 and 2013. It is remarkable that in this new study only older data up to 2008 is re-analyzed without incorporating this newly acquired data.

Figure 2. An overview of mass balance estimates of Antarctica from various studies. Each box represents the time interval (width) as well as reported uncertainty (height) of the estimates. The brown boxes, falling outside all other estimates, represent the outcome of the new Zwally et al. study. Source: Luke Trusel, Woods Hole Oceanographic Institution.

At present the newly released study stands alone in its claim of ice gain in Antarctica, contradicting the bulk of scientific literature of the last decade, including other NASA studies, using in part the same data or completely different methods. At first it remains to be seen whether the conclusions of this study will hold after more thorough scientific evaluation. In that respect it should also be noted that the conclusions are not specifically endorsed by NASA as portrayed in many of the media reports. Nevertheless, if the conclusions are right than it actually raises many new and interesting questions, such as, if not from Antarctica, where does the part of sea level rise thus far ascribed to it come from? Perhaps the part of other sea level rise contributors has been underestimated thus far. In that case we could even end up with more sea level rise if in the coming decades Antarctica does not act as a buffer anymore as the study suggests.

In contrast to their claims, we demonstrate in our comment on this article that the IPCC correctly placed the hottest decade in the context of long-term trends. The IPCC did not dismiss the recent slowdown in surface warming, the so-called “hiatus” or “pause”, as scientifically irrelevant.

Hollin and Pearce’s central premise is nicely encapsulated in the abstract of their paper:

Here we demonstrate that speakers at the press conference for the publication of the IPCC’s Fifth Assessment Report (Working Group 1) attempted to make the documented level of certainty of anthropogenic global warming (AGW) more meaningful to the public. Speakers attempted to communicate this through reference to short-term temperature increases. However, when journalists enquired about the similarly short ‘pause’ in global temperature increase, the speakers dismissed the relevance of such timescales, thus becoming incoherent as to ‘what counts’ as scientific evidence for AGW.

This observation leads them to theorize about the tension between scientific certainty and meaning. But did they actually demonstrate what they claimed they did? We argue in a comment to this article that they did not.

They base their statement that IPCC speakers attempted to communicate ‘meaning’ by reference to short-term temperature increases on this statement made by Pachauri:

the decade 2001 onwards having been the hottest, the warmest that we have seen

This statement was explicitly placed in the context of long-term, climatically relevant trends, as indicated by Pachauri’s preceding words and the graph below (IPCC AR5 SPM fig 1) that was prominently shown at the press conference:

each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850

That is an entirely different ballgame than the short-term variability that underlies the slowdown of the surface warming trend (often referred to as “the pause”). So no, they did not demonstrate in the least that IPCC speakers “relied on temporally local events to increase public meaning”. Hollin and Pearce’s premise is based on misunderstanding the timescales that were discussed.

What about the claim that IPCC speakers dismissed the relevance of the so-called “pause”?

As we write in our comment, five of the 18 journalists asked a question about recent temperature trends; none were ignored. Also David Rose’s question, which is featured prominently in Hollin and Pearce’s argument, was not dismissed. Stocker responded to Rose’s question, followed by Jarraud explaining why he regarded it as “ill-­‐posed”, reframing it as a well-posed question, and responding to that. See the (freely available) Supplemental Information for more details.

So no, Hollin and Pearce did not demonstrate that the relevance of the slowdown was dismissed. Hotwhopper hammers home this and related points with lots of extra detail, showing that the IPCC message was clearly received by most journalists and that only one journalist who asked a question at the press conference “condemned” the IPCC for supposed dismissal. This journalist, as you might suspect, was David Rose, for whom IPCC bashing is a modus operandi.

The entire premise for their argument thus seems to rest on shaky ground. Their conclusions about e.g. the IPCC’s credibility being somehow eroded by their (in Hollin and Pearce’s eyes) mixed messages are thus not supported.

I’m actually surprised that in their reply to our comment, Hollin and Pearce don’t acknowledge their mistaken interpretation regarding timescales, but rather keep digging their heels in regarding that point. E.g. they reiterate that Pachauri’s quote above was “illustrative of references to the warmest decade made by all three speakers”, apparently without realizing, or not considering it as relevant, that this and other such references were made in the context of the long-term trend. Very peculiar.

They wrote a blogpost in which they try to reflect on the meaning of this back and forth in the scientific literature. It’s an interesting read, and they basically argue that their initial letter was based on inductive research: starting with the data, seeing patterns or interesting things, and the theories and broader claims are integrated later. They claim that this is more common in qualitative social science than it is in natural science and that this difference may be at the root of our disagreement. I’m actually quite comfortable with such inductive style research. I have often started my research by looking at “what the data told me” as my PhD advisor used to say, especially for a large body of field observations. That was also the approach we took in analyzing the data from our climate science survey.

And Then There’s Physics, also co-author of the response to Hollin and Pearce, goes into more detail on this point, and rightly wonders

why it makes any difference whether one’s approach is inductive or deductive. What you present should be a reasonable representation of reality, whether you approached it inductively (“the data looks interesting, why is that?”) or deductively (“I have a theory/hypothesis, let me collect some data to test it”). For example, either the IPCC fell into a trap by using one indicator to stress the certainty of AGW while dismissing another essentially equivalent indicator, or they didn’t; either the IPCC dismissed the so-called “pause”, or they didn’t. It can’t really be both.

I would hardly think that the difference in interpretation between Hollin and Pearce on the one side and Jacobs et al (myself included, but also e.g. cognitive psychologist Stephan Lewandowsky) on the other side boils down to a typical difference in approach between social science and natural science. Rather, it boils down to the former misinterpreting statements relating to timescales and basing the whole remainder of their argument on a false premise.

I re-read your reply incl the SI and I’m still struggling to see understand your point of view regarding time scales.

Greg,

In the SI for example you quote Jarraud as saying
“more temperature records were broken than in any other decade”

with the emphasis (italics) on the word “any”. Doesn’t that point to these temperature record being presented in the context of the longer-term trend (“than in *any* other decade”)? To me the answer to that would be a clear yes, but apparently that’s not the same to you. Could you clarify your position in that respect?

It may very well be that speakers mentioned (spatially and temporally) local events as *examples* of what climate change might mean to a person’s live, so yes, to make it more societally meaningful. I’m not challenging that. What I’m challenging is your premise that in doing so the IPCC speakers provided an incoherent picture of timescales, on the one hand presenting a decade’s worth of data as scientifically meaningful and on the other hand as not meaningful. The former, the warmest decade, was consistently put in the context of the long term trend, even in the quote that you mentioned yourself. So there was no such incoherence.